SOME INVESTIGATIONS INTO RESISTANCE SPOT WELDING OF AUSTENITIC STAINLESS STEEL

Abstract

Influence of welding parameters such as weld current, weld time and electrode force on weld quality of resistance spot welds of austenitic stainless steel sheets ( 2 mm thick ) has been studied. Mechanical characteristics of spot welds has been assessed by performing tensile shear and fatigue tests. Separate tests were carried out for each variable. Tensile shear strength increases with increase in weld current, weld time and electrode force. Metal expulsion has been observed at excessive weld current, weld time and extremely low- electrode force. Metal expulsion weakens the spot welds. That is why, A reduced failure load has been observed at excessive weld current and weld time. A reduced shear strength has also been observed at higher electrode force. Fatigue life shows similar trend as in case of tensile shear strength. Qualitative characteristics of spot welds has been assessed by measuring size of, weld nuggets & HAZ, degree of electrode indentation and hardness of weld nugget and HAZ. Weld nugget diameter, width of HAZ and degree of electrode indentation increase with increase in weld current, weld time and electrode force. Hardness of weld nugget and HAZ decreases with increase in weld current, weld time and electrode force. Metallographic examination reveals columnar structure in weld nugget. Grains in HAZ adjacent to fusion line has been coarsen. Width of recystallized zone of HAZ has been increased with increase in weld current and weld time. Shrinkage cavity has been observed in centre of weld nugget at higher weld current.